Why did George Lucas choose not to include the scene in Return of the Jedi, where Luke Skywalker learns how to build a Lightsabre?

It would have been interesting to see how a young impatient Jedi Padawan would learn the skills and abilities needed to create such a finely crafted instrument. Did he have have help from the ghost of Obi-Wan? Was he simply reading from the notes that Obi-Wan might have left him?

In fact, it would be interesting at some point , to learn the diferences between the processes involved in creating a Sith Lightsabre, and a Jedi Lightsabre. It's not that I am simply a techno-nerd that like to know every detail - it would just be great if fan-fiction authors like myself had something that was considered "canon" to work with. such background details can be the threads that tie a plotline together.